16 The Principles of Fruit-growing. 
“In observing trees in continuous severe winter 
weather, my attention has often been ealled to the 
fact that the twigs seem somewhat duller and more 
somber than usual, and in some eases tend to shrivel 
up and have the appearance of drying out. When 
a warm spell comes, this condition changes, and the 
twigs become brighter and seem to freshen up, and 
sometimes I imagine that they become more plump. 
The freshening-up feature is especially noticeable on 
large clumps or groves of willow; the twigs usually 
take on a much brighter color during warm spells 
in winter than during the continued freezing weather. 
During thawing weather, the equilibrium is main- 
tained between the moisture or sap in the tree top 
and that taken in by the roots, and as fast as mois- 
ture evaporates from the tree top, sap flows up from 
the roots and the equilibrium is re-established. In 
freezing weather, the moisture, even though frozen, 
is probably evaporating from the tree tops; and 
the sap, being frozen, does not flow up from the 
roots and replace the evaporated moisture. Thus 
the equilibrium between the tree tops and roots is 
unbalanced, and it is at this time that the twigs 
become shriveled hy reason of moisture being lost 
and not replaced. 
“In support of these statements, I made the fol- 
lowing investigation: After several days of con- 
tinuous freezing weather, and at a time when I 
expected a thaw, I cut twigs of a variety of trees 
and estimated the percentage of moisture contained 
in them. Again, just as soon as a thaw came, I eut 
